The present invention relates generally to adhesives for flat panel displays and optoelectronics components. Still more specifically, the present invention relates to stable, thermally curable, single component acrylate resin adhesives for flat panel displays and optoelectronics components.
In the fields of flat panel displays and optoelectronics, a wide variety of adhesives and sealant formulations are used for bonding components together. Specifically, adhesives are used to bond large display elements together and for sealing edges in flat panel displays. Further, in optoelectronics components, various elements of laser diodes and dense wave division multiplexing assemblies are bonded together using adhesives. Typically, adhesives are either thermally curable (i.e., heat curable) or curable using ultraviolet light (UV-curable). Acrylate resins are currently available for use in adhesive applications. Currently available acrylate formulations are UV-curable. As they are effective adhesives for components of flat panel displays and optoelectronics devices, UV-curable acrylate adhesives are widely used. However, these adhesives cannot be employed to bond opaque components together. In order for any UV-curable adhesive to be used, at least one of the components needs to be transparent or semi-transparent. Thus, UV-curable acrylate adhesives cannot be used to bond ceramic parts, metallic parts or other opaque parts together. For these opaque parts, manufacturers are forced to use a thermally curable adhesive.
In the fields of flat panel displays and optoelectronics products, the currently available heat curable adhesives are epoxy materials. While epoxy materials are effective adhesives, they suffer from a number of disadvantages. First, thermally-curable epoxy materials are typically provided as two separate components and then mixed together prior to use. The mixed formulations have a short pot life, typically 4 to 8 hours after mixing. If the manufacturer cannot use all of the mixed thermally-curable epoxy material within the 4 to 8 hour time span, the material is wasted. Accordingly, considerable waste is associated with thermally-curable epoxy adhesives.
While single component (i.e., no need for mixing) thermally-curable epoxies are available, these materials are not room temperature stable. They must be shipped and stored at low temperatures in freezers. Thus, due to the difficulties in shipment and handling of these unstable materials, and further due to their instability at room temperature, the use of single component thermally-curable epoxy-based adhesives is not economical.
Finally, because many components of flat panel displays and optoelectronics devices are opaque and many are transparent, and further because manufacturers prefer to use UV-curable resins if possible, the assembly of many flat panel display devices and optoelectronics devices involve the use of at least two different adhesives, UV-curable and heat-curable. The two different adhesives often get confused on the assembly floor causing waste and other inefficiencies.
Accordingly, there is a need for an improved adhesive that can be provided as a single component liquid that is stable at room temperature and that is heat curable.
Further, there is a need for an improved adhesive that is a stable liquid at room temperature and further that can be either heat-cured or UV-cured.
The present invention satisfies the aforenoted needs by providing a single component, i.e., liquid, heat-curable adhesive formulation that comprises from about 5 to about 70 wt % of at least one acrylate monomer, from about 5 to about 94 wt % of an acrylate oligomer, from about 0.1 to about 10 wt % of a thermal initiator selected from the group consisting of diacyl peroxides, benzoyl peroxides and peroxy esters. The above formulation of the present invention is a stable liquid at room temperature with a shelf life ranging from about one month to about one year or longer.
In a refinement of the invention, the thermal initiator is selected from the group consisting of lauroyl peroxide, benzoyl peroxide, decanoyl peroxide, di(n-propyl)peroxydicarbonate, di(sec-butyl)peroxydicarbonate, t-butyl peroxyneodecanoate, di-t-butyl peroxide, di-t-amyl peroxide, (t-butylperoxy)butyrate, t-butyl peroxybenzoate, and di-t-butyl peroxyoxalate. The thermal initiator may also be a hyponitrite, such as di-tert-butyl hyponitrite.
In a further refinement, the formulation further comprises a thickening agent.
In a further refinement, the formulation further comprises an acrylate cross-linking monomer. In a further refinement of this concept, the acrylate cross-linking monomer is selected from the group consisting of tris(2-hydroxy-ethyl)isocyanate triacrylate, neopentylglycol diacrylate, hexandiol diacrylate, triethyleneglycol dimethacrylate.
In another refinement, the formulation further comprises a cross-linkable adhesion promoter. In a further refinement of this concept, the adhesion promoter is selected from the group consisting of polyazarnide silane, aminoalkyl silane, gamma-mercaptopropyltrimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, gamma-methacryloxypropyltrimethoxysilane, and bis-(3-[triethoxysilyl]propyl) tetrasulfane.
In yet another refinement, the adhesion promoter comprises a titanium salt or a zirconium salt.
In another refinement, the formulation further comprises an inhibitor.
In another refinement, the acrylate monomer is selected from the group consisting of isobornyl acrylate, phenoxyethyl acrylate, isoctyl acrylate, propoxylated allyl methacrylate and tetrahydrofurfuryl acrylate.
In yet another refinement, the at least one acrylate monomer comprises isobornyl acrylate and phenoxyethyl acrylate. In a further refinement of this concept, the isobornyl acrylate is present in an amount ranging from about 6 to about 10 wt %. In yet a further refinement, the isobornyl acrylate is present in an amount of about 8 wt %. In still another refinement, the phenoxyethyl acrylate is present in an amount ranging from about 12 to about 20 wt %. In yet a further refinement, the phenoxyethyl acrylate is present in amount of about 16 wt %.
In another refinement, the acrylate oligomer is polyurethane acrylate. In a further refinement of this concept, the polyurethane acrylate is present in an amount ranging from about 55 to about 75 wt %. In still a further refinement, polyurethane acrylate is present in an amount of about 66.6 wt %.
In another refinement, the thermal initiator is benzoyl peroxide which is present in an amount ranging from about 1 to about 5 wt %. In still a further refinement of this concept, the benzoyl peroxide is present in an amount of about 1.5 wt %.
In another refinement, the formulation comprises a photo initiator which enables the formulation to be either heat-cured or UV-cured. In a further refinement of this concept, the photo initiator is benzil dimethyl ketal which is present in an amount ranging from about 2 to about 4 wt %. In still a further refinement of this concept, the benzil dimethyl ketal is present in an amount of about 3 wt %.
In another refinement, a single component liquid heat-curable adhesive formulation is disclosed which comprises from about 6 to about 10 wt % isobornyl acrylate, from about 12 to about 20 wt % phenoxyethyl acrylate, from about 60 to about 70 wt % polyurethane acrylate, and from about 0.5 to about 2.5 wt % of a thermal initiator selected from the group consisting of diacyl peroxides, benzoyl peroxides and peroxy esters. The above formulation is a stable liquid at room temperature.
In still a further refinement, a single component liquid heat-curable adhesive formulation is disclosed which comprises from about 8 to about 12 wt % isooctyl acrylate from about 3 to about 7 wt % propoxylated allyl methacrylate, from about 70 to about 80 wt % polyester acrylate and from about 0.5 to about 2.5 t-butyl peroxybenzoate. In a further refinement of this concept, the formulation further comprises from about 6 to about 10 wt % neopentyl glycol diacrylate and from about 0.5 to about 1.5 gamma-aminopropyltriethoxysilane.
In another refinement, a single component liquid heat-curable adhesive formulation is disclosed which comprises from about 9 to about 13 wt % tetrahydrofurfuryl acrylate, from about 60 to about 70 wt % epoxy novolak acrylate and from about 0.5 to about 2.5 wt % lauroyl peroxide. In a further refinement of this formulation, the formulation further comprises about 10 to about 14 wt % neopentyl glycol diacrylate as a cross-linking agent, from about 8 to about 12 wt % triethylene glycol diacrylate as a cross-linking agent, from about 0.5 to about 1.5 wt % gamma-mercaptopropyltrimethoxysilane as an adhesion promoter and approximately 0.1 wt % 4-methoxyphenol as a stabilizer.
In yet another refinement, a single component liquid heat-curable adhesive formulation is disclosed which comprises from about 9 to about 13 wt % tetrahydrofurfuryl acrylate, from about 57 to about 67 wt % aromatic urethane acrylate and from about 1 to about 2 wt % di-t-butyl peroxyoxalate. In a further refinement of this formulation, the formulation may further comprise from about 10 to about 14 wt % hexandiol diacrylate as a cross-linking agent, from about 8 to about 12 wt % triethylene glycol dimethacrylate as cross-linking agent, from about 1 to about 3 wt % benzophenone and/or from about 1 to about 3 wt % triethylamine as photo initiators, from about 0.5 to about 1.5 wt % octyltriethoxysilane as an adhesion promoter and less than 1 wt % phenothiazine as a stabilizer.
Any of the above formulations may also include stabilizers selected from the group consisting of 4-methoxyphenol, butylated hydroxytoluene (2,6-di-t-butyl-4-methylphenol), phenothiazine, bistridecylthiodipropionate, and hindered amines.
In another refinement, a method of adhering a first component of a flat panel display to a second component of a flat panel display is disclosed. The method comprises providing a room temperature stable liquid heat-curable adhesive formulation that comprises from about 5 to about 70 wt % of at least one acrylate monomer, from about 5 to about 94 wt % of an acrylate oligomer, and from about 0.1 to about 10 wt % of a thermal initiator selected from the group consisting of diacyl peroxides, benzoyl peroxides and peroxy esters. The method further comprises applying the formulation to the first component, engaging the second component with the first component with the formulation disposed therebetween and heat-curing the formulation.
In yet another refinement, a method of adhering a first component of an optoelectronics device to a second component of an optoelectronics device is disclosed. The method comprises providing a room temperature stable liquid heat-curable adhesive formulation comprising from about 5 to about 70 wt % of at least one acrylate monomer, from about 5 to about 94 wt % of an acrylate oligomer and from about 0.1 to about 10 wt % of a thermal initiator selected from the group consisting of diacyl peroxides, benzoyl peroxides and peroxy esters. The method further includes the step of applying the formulation to the first component, engaging the second component to the first component with the formulation disposed therebetween and heat-curing the formulation.